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Journal of Nanomaterials
Volume 2008 (2008), Article ID 769250, 8 pages
http://dx.doi.org/10.1155/2008/769250
Research Article

The Ultimate Ballistic Drift Velocity in Carbon Nanotubes

1Department of Electronic Engineering, Faculty of Electrical Engineering, Universiti Teknology Malaysia, 81310 Skudai, Johor Darul Takzim, Malaysia
2Electrical Engineering Division, Engineering Department, University of Cambridge, 9 J.J. Thomson Avenue, Cambridge CB3 0FA, UK
3Department of Electrical and Computer Engineering, Wilkes University, Wilkes-Barre, PA 18766, USA

Received 12 February 2008; Revised 24 June 2008; Accepted 6 August 2008

Academic Editor: Theodorian Borca-Tasciuc

Copyright © 2008 Mohammad Taghi Ahmadi et al. This is an open access article distributed under the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.

Abstract

The carriers in a carbon nanotube (CNT), like in any quasi-1-dimensional (Q1D) nanostructure, have analog energy spectrum only in the quasifree direction; while the other two Cartesian directions are quantum-confined leading to a digital (quantized) energy spectrum. We report the salient features of the mobility and saturation velocity controlling the charge transport in a semiconducting single-walled CNT (SWCNT) channel. The ultimate drift velocity in SWCNT due to the high-electric-field streaming is based on the asymmetrical distribution function that converts randomness in zero-field to a stream-lined one in a very high electric field. Specifically, we show that a higher mobility in an SWCNT does not necessarily lead to a higher saturation velocity that is limited by the mean intrinsic velocity depending upon the band parameters. The intrinsic velocity is found to be appropriate thermal velocity in the nondegenerate regime, increasing with the temperature, but independent of carrier concentration. However, this intrinsic velocity is the Fermi velocity that is independent of temperature, but depends strongly on carrier concentration. The velocity that saturates in a high electric field can be lower than the intrinsic velocity due to onset of a quantum emission. In an SWCNT, the mobility may also become ballistic if the length of the channel is comparable or less than the mean free path.